Security seals are widely used to demonstrate the integrity of a closed container, truck, roll pallet, cage or box to demonstrate, for example, that they have not been opened during transit. Typically such security seals are made from plastics material and comprise a strap with a plug at one end and a socket at the other end. The socket includes a one-way lock. In this way, the security seal is threaded through a locking point and the plug inserted into the socket. The plug is then locked irremovably into the socket so that the only way in which the security seal can subsequently be removed is by destroying it. Typically the security seal includes a unique serial number so that it can be confirmed that the same seal is still present after transport as was applied before transport, and the security seal may include a flag portion to carry this serial number.